During handling and wear, contact lenses are susceptible to the accumulation of a variety of materials which may adhere to the surface of the lens and/or lodge within and adhere chemically and/or spatially to the inner bulk matrix of the lens. For example, during wear, lenses contact proteinaceous materials such as lysozyme and mucoproteins, both of which are constituents of lachrymal tears, and lipids such as sterols, waxes, glycerides, phospholipids, fatty alcohols and acids.
If contact lenses are not properly cleaned, lysozyme, mucoproteins and other soils can accumulate on and/or in the lens to a point where the lens wearer begins to feel discomfort, for example due to altered lens fit, the lens spectral characteristics are adversely affected, for example through discoloration due to the deposits, disinfection may be impeded, and the gas permeability may be decreased. Such soiling decreases the overall estimated useful lifetime of the lens.
Certain types of cleaning or disinfecting techniques and compositions have been found inadequate for inhibiting and reducing the formation of these deposits on hydrophilic contact lenses. For example, it has been shown that sterilization techniques such as heat in the form of boiling water or steam can have adverse effects on soft lenses. High temperatures may cause tear proteins to be baked onto the contact lens polymer, resulting in difficulties in cleaning. Heat sterilization techniques also tend to accelerate lens buildup by precipitating absorbed proteinaceous materials. Sterile saline solutions have limited effect on the removal of soils, thus, requiring some additional cleaning procedure. Peroxides, which are effective disinfectants against ocular pathogens, have also been found to be inadequate for removing lens soils.
Attempts have been made to reduce and inhibit the tendency for proteins to adhere to a lens surface. For example, U.S. Pat. No. 4,168,112 to Ellis discloses forming a thin ionic polymeric coating on a contact lens having an ionically charged surface. The coating is electrostatically bound to the lens surface and reduces the tendency for mucoproteins to adhere to the lens surface. Ellis shows contact lens solutions containing cationic polymers for forming a hydrophilic polyelectrolytic complex on the lens surface wherein the complex acts as a hydrogel "cushion." Other additives to the lens solutions shown by Ellis include preservatives such as ethylenediaminetetraacetic acid (EDTA).
U.S. Pat. No. 4,414,127 to Fu discloses compositions which degrade and remove proteinaceous deposits from all types of contact lens plastics by chemically degrading these deposits into water-soluble proteins. Fu shows using metal chloride salts as catalysts for peroxide decomposition where the peroxide is used in a contact lens cleaning solution.
U.S. Pat. No. 4,259,202 to Tanaka discloses a solution used for cleaning and preserving contact lenses. The solution of Tanaka contains as an effective ingredient a particular monoester of saccharose with a fatty acid. The solution also contains an alkali metal salt of a saturated fatty acid and a compound selected from the group consisting of a polysaccharide and a polysaccharide derivative. Examples of the polysaccharide and its derivative include alkali metal salt of alginic acid, xanthan gum, alkali metal salt of carboxymethyl cellulose, hydroxypropyl methylcellulose and alkali metal salt of chondroitin sulfuric acid.
Bendazac lysine, an anti-cataract drug, has been found to limit protein deposition on soft contact lenses. See Missiroli, A., Ricci, F., Pocobelli, A., Cedrone, C., Cerulli, L., CLAO Journal (Contact Lens Association of Ophthalmologists), April 1991, 17(2) pp. 126-8. Bendazac lysine is an oxyacetic acid with known anti-inflammatory, antinecrotic, choleretic and antilipidaemic properties, but it is said that its principal effect is to inhibit the denaturation of proteins.
It would be desirable to provide an improved system for inhibiting and/or reducing the deposition of lysozyme and other protein on contact lenses, such as hydrophilic contact lenses. Desirably, the improved method would provide the contact lens wearer with an indication that the lens has been so treated and would facilitate handling of the treated lens by increasing lens visibility. It would also be desirable to provide a system which would provide the contact lens wearer with a periodic reminder to repeat the contact lens treatment. It would also be desirable to provide a system which would allow the user to detect visually the presence of protein deposits on contact lenses, thus prompting more vigorous cleaning of the lenses.